1. Field of the Invention
This invention relates to gas generators or inflators, and more particularly, to self-contained radial gas generators for inflating large passenger side occupant restraint airbags or crash bags where such generators utilize the combustion of solid gas generant compositions for the rapid generation of the inflating gas.
2. Description of the Prior Art
Self-contained, single stage gas generators or inflators for automobile passenger side airbags that utilize combustible solid gas generant compositions are known in the prior art. A radial form of such generator is disclosed in U.S. Pat. No. 4,296,084 that was issued on Oct. 20, 1981 to G.V. Adams et al., which patent is assigned to the assignee of the present invention. The disclosure of U.S. Pat. No. 4,296,084, by reference, is incorporated herein. Common features of such generators are the inclusion in a single combustion chamber of a gas generant composition containing a pelletized alkali metal azide and means to filter and to cool the gas positioned between the gas generant composition and gas discharge orifices or outlet holes, as defined by the inflator housing. Such gas generant compositions are considered advantageous for use in automobile airbag inflating applications because the product of the combustion is mainly nitrogen, an inert gas. The speed of reaction or burning of such compositions may be selected to be such as to effect the generation of gas at a very rapid rate but without detonation.
A problem has been encountered with single stage, that is, single combustion chamber, passenger side radial gas generators. The single combustion chamber passenger side radial generators known in the prior art tend to perform at an initial pressure rise rate which is greater than desirable in the zero to twenty (0 to 20) millisecond time frame after inflator initiation. The initial rapid pressure rise has been identified as a possible cause for injuries to an out-of-position occupant, and in particular, a child, during deployment of the airbag.
In U.S. Pat. No. 3,663,035 issued to Thomas W. Norton on May 16, 1972, there is disclosed a crash bag inflator comprising a two-stage gas generator, wherein a first stage is ignited to provide an initial deployment thrust at a time prior to ignition of a second stage. The two-stage gas generator, as described, consists of a pair of first and second inflators that are positioned in parallel relation, being held together by a tie bar. Each stage has one end attached to a block in which an ignition cavity common to both stages is provided. A fixed delay line operatively separates the second stage from the ignition cavity and delays ignition of the second stage by a few milliseconds. Both stages are said to be fully operative within less than ten (10) milliseconds of initiation by a pyrotechnic initiator responsively to a crash.
While described as providing a more controlled delivery of gas to an airbag without disadvantageously delaying the deployment thereof, the Norton two-stage gas generator structure is complex and bulky and requires a volume of space larger than desirable for installation on the dashboard of an automotive vehicle.
Thus, there is a need and a demand for improvement in passenger automotive restraint gas generators that have particular utility in protecting the out-of-position passenger and that are of maximum compactness, requiring a minimum volume of space for installation on the passenger side of an automotive vehicle. The present invention was devised to fill the technological gap that has existed in the art in this respect.